Four of the most advanced U.S. fighter jets flew over South Korea on Wednesday in a clear show of force against North Korea, a day after South Korea’s president warned of the North’s collapse amid a festering standoff over its nuclear and missile ambitions.

The stealthy, high-tech F-22 planes capable of sneaking past radar undetected landed at Osan Air Base near Seoul after the flyover escorted by other U.S. and South Korean fighter jets.

Pyongyang will likely view the arrival of the planes flown from a U.S. base in Japan as a threat as they are a display of U.S. airpower apparently aimed at showing what the United States can do to defend its ally South Korea from potential aggression from North Korea.

“The F-22 ‘Raptor’ is the most capable air superiority fighter in the world, and it represents one of many capabilities available for the defense of this great nation,” Lt. Gen. Terrence J. O’Shaughnessy, deputy commander of the U.S. military command in South Korea, said in a statement.

“The U.S. maintains an ironclad commitment” to the defense of South Korea, he said.

The U.S. military would not say how long the F-22s will be deployed in South Korea.

The United States often sends powerful warplanes to South Korea in times of tension with North Korea. Last month it sent a nuclear-capable B-52 bomber to South Korea after North Korea defiantly conducted its fourth nuclear test.

The international standoff over North Korea deepened earlier this month when Pyongyang ignored repeated warnings by regional powers and fired a long-range rocket carrying what it calls an Earth observation satellite. Washington, Seoul and others consider the launch a prohibited test of missile technology.

Foreign analysts say the North’s rocket launch and nuclear test put the country further along it its quest for a nuclear-armed missile that could reach the U.S. mainland.

South Korea’s president on Tuesday warned North Korea faces collapse if it doesn’t abandon its nuclear bomb program, an unusually strong broadside that is certain to infuriate Pyongyang.

In a speech at parliament, President Park Geun-hye said South Korea will take unspecified “stronger and more effective” measures to make North Korea realize its nuclear ambitions will result only in accelerating its “regime collapse.”

Park made the speech while defending her government’s decision to shut down a jointly run factory park in North Korea in response to the North’s rocket launch. Pyongyang retaliated by expelling all the South Koreans there, put its military in charge of the area and cut off key communication hotlines between the Koreas.

It is unusual for a top South Korean official to publicly touch on such a government collapse because of worries about how sensitive North Korea is to talk of its authoritarian government losing power. Pyongyang has long accused Washington and Seoul of agitating for its collapse.

After the rocket launch, Seoul announced that talks would begin with Washington on deploying a sophisticated U.S. missile defense system in South Korea and that the allies’ annual military drills in the spring will be the biggest ever.

The deployment of the Terminal High-Altitude Area Defense, or THAAD, is opposed by North Korea, China and Russia. Opponents say the system could help U.S. radar spot missiles in other countries.

Pyongyang has also called regular U.S.-South Korea military exercises a rehearsal for a northward invasion. The allies say their drills are defensive in nature.

(AP)